Period-24 glider gun is a true period 24 gun discovered by Noam D. Elkies in 1997.^{[1]} It uses four large period4oscillators (two of them variants of fountain, the other two adjoined by common casing) to hassle two T-tetrominos, which react together to produce gliders. The form on the right is a reduced variant found by Karel Suhajda.^{[2]}
No more than five days after the initial discovery, Elkies found a method to double the period of the gun, resulting in the first known period 48 glider gun.^{[1]} A smaller version was found in 2016 by Tanner Jacobi, using Rich's p16 to double the period.^{[3]}